ASA 126th Meeting Denver 1993 October 4-8

Loud launch noise and sonic booms from some military space vehicle
launches from Vandenberg Air Force Base impact pinnipeds on the mainland and at
San Miguel Island, California, and may cause stampedes, temporary threshold
shift or, less likely, permanent hearing damage. Maximum fast A-weighted (MFXA)
sound levels approximately 4.8 miles downrange during the launch of three Titan
IV rockets were 93.2, 92.7, and 93.0 dB; average sound exposure levels were
between 98.9 and 101 dB. Harbor seals fled into the water in response but many
returned to land within several hours. A sonic boom was recorded at San Miguel
Island during one launch. Its peak flat sound-pressure level was 129.5 dB and
maximum fast A-weighted sound level was 86.2 dB; virtually all of the energy
was below 500 Hz. Pinniped behavioral responses were mild and brief. Predicted
overpressures for focused sonic booms from the Titan IV rocket are
substantially greater ((greater than or equal to)150 dB). Noninvasive hearing
tests using ABR and OAE techniques are being used to determine if pinnipeds
suffer temporary threshold shifts or permanent hearing damage from exposure to
those sonic booms.